The present invention relates generally to the field of tube extraction, and more particularly to an improved method of facilitating the removal of tubes from structures comprising tube sheets, such as boilers, condensers, evaporators, drums, and the like.
A typical heat exchanger comprises a pair of parallel tube sheets, a plurality of baffle plates, and a plurality of heat exchanger tubes. The tube sheets are located at the ends of the heat exchanger. The baffle plates are positioned between the tube sheets and generally parallel thereto. The tubes extend between the tube sheets and through the baffle plates and are supported by the tube sheets. The tube sheets and baffle plates have a series of aligned holes formed therein, and the tubes are inserted through these holes and then expanded in the areas of the tube sheets into fluid-tight pressure contact therewith.
Because of malfunctions or normal preventive maintenance, it may be necessary to remove one or all of the tubes from the structure. To replace the tubes they are generally cut between the tube ends and the expanded ends of the tubes forcibly withdrawn from the tube sheets an inch or two until they can be withdrawn by hand.
Various tools have been suggested for removing these tubes by using wedges that are driven inside a bore of a structure, expanded for engaging the inside wall of a tube and retracted for pulling the tube out of the bore.
U.S. Pat. No. 4,355,450 to Miller discloses a tube extracting mechanism having a wedge with expandable circumferential gripping teeth.
U.S. Pat. No. 3,791,011 to Keys shows a tube pulling device with longitudinally fixed radially expanding gripping means which engages the tube wall for withdrawal of the tube from the tube sheet.
U.S. Pat. No. 3,507,028 to Stellatella shows a hydraulic tube puller with radial expansion of an inner end portion at a tube gripping member into the tube wall.
The primary problem with all these prior art structures is the imposition of expansion force on the tube precisely at the point where it is engaged with the tube sheet which can damage the metal between adjacent holes and cause the holes in the tube sheet to enlarge and not properly grip a new tube when it is expanded. Moreover, the prior art devices require additional moving parts which increase the likelihood of malfunctions and breakage of the device, which results in an increase of down-time of the structure for repairs.
The method of the present invention does not expand the tube ends radially but softens the tube and utilizes tensile forces to longitudinal compress the tube being extracted, and possesses many other advantages over the prior art as discussed herein.